Power quality is an increasing problem in mains electrical distribution systems with the addition of many different modern electrical appliances and electronic devices. In an Alternating Current (AC) mains electrical system, there is an alternating positive and negative sine voltage wave, at either 50 or 60 Hz frequencies, depending on the country. In an AC system, the current also has a sine waveform, but has a particular phase angle in relation to the voltage waveform. It is well know that as inductive loads are connected to the electrical system, the current begins to lag the voltage waveform due the reactance of the inductive load. The phase difference between the voltage and the current is related as a Power Factor (PF). When the voltage and current are correctly in phase, the PF equals to one (PF=1). As inductive loads are added, the PF falls as the current begins to lag the voltage waveform. This causes serious consequences in terms of electricity cost, and penalties that can be levied for a low PF, which adds to the costs of electrical generation and transmission. For example, at PF<0.7, the heavy levies and additional charges can begin to pass down to billings to end users.
There are passive power quality compensation devices that rely on switching in various line capacitors across the electrical system phases that compensate for the inductive loads, and correct the PF back to high levels closer to 1, hence restore the power quality. With these passive power quality compensation devices, first, the PF is measured; second, the amount of the capacitance required is calculated by various means, such as deriving from a look-up table, minimum and maximum limits, etc.; then finally the amount of capacitance is switched in.